The invention relates to a polishing composition for chemical mechanical planarization, CMP, to remove a metal layer from a semiconductor substrate, further described as, a semiconductor wafer.
Large numbers of semiconductor devices are built from different materials that are successively deposited in successive layers on a wafer of silicon, which provides a semiconductor substrate. The semiconductor devices include semiconductor circuit elements and electrically conducting circuits, further described as, interconnects. The interconnects comprise metal in trenches of precise dimensions. The trenches are recessed in a surface of a dielectric layer on the wafer, also known as, an interlayer. The trenches are manufactured according to known photolithographic etching processes. A barrier film is deposited over the underlying dielectric layer and the trenches. The metal that fills the trenches to provide the interconnects is applied as a layer of metal that is deposited on the underlying barrier film.
CMP is a process performed with a moving polishing pad applied with a downforce against the layer of metal, while an aqueous polishing composition is interposed between the polishing pad and the surface being polished. The layer of metal is removed by a combination of abrasion and chemical reaction. CMP is performed to remove the layer of metal from the underlying barrier film, while minimizing removal of the metal in the trenches, thus, minimizes dishing of the interconnects. Dishing is a name applied to recesses that result from undesired removal of some of the metal in trenches by the CMP operation. Excessive dishing comprises defects in the interconnects.
According to EP 0 913 442, a polishing composition is provided with polyacrylic acid to minimize removal of metal in trenches during CMP, thus, minimizing dishing.
A polishing composition is desired to minimize removal of metal in trenches during CMP, while maximizing a removal rate of the metal layer during CMP.
The invention resides in a polishing composition, further described as, an aqueous composition, for polishing a semiconductor substrate with both the aqueous composition and a polishing pad applying a downforce, to remove metal from an underlying barrier film on the semiconductor substrate, the aqueous composition comprising:
a pH no higher than 5,
an oxidizer of the metal at said pH to provide ions of the metal,
a complexing agent to dissolve the ions,
a carboxylic acid polymer reactive with the metal while the polishing pad applies a relatively higher downforce on the metal in a metal layer on the underlying barrier film, to provide a relatively high removal rate of the metal layer,
the carboxylic acid polymer being reactive with the metal in trenches while the polishing pad applies a relatively lower downforce on the metal in trenches, which tends to provide a relatively high removal rate of the metal in trenches, and
a combination of a metal corrosion inhibitor and a surfactant, which adsorbs on the metal in trenches on which the relatively lower downforce is applied, to minimize the removal rate of the metal in trenches, as would tend to be provided by the carboxylic acid polymer and the applied downforce without the combination of the metal corrosion inhibitor and the surfactant.
The terminology, surfactant, is interpreted to mean, a surface active agent that adsorbs to a surface and lowers a surface tension of a liquid on the surface. According to an embodiment, a surfactant comprises, an anionic surfactant as distinguished from a cationic surfactant, and as distinguished from a neutral charge surfactant.
According to another embodiment, a surfactant comprises, a sulfonate surfactant comprised of molecules having at least six carbon atoms, as distinguished from a sulfonate comprising molecules having an insufficient number of carbon atoms to exist as a polymer in the polishing composition.
According to another embodiment, a surfactant comprises, an alkali metal organic sulfonate.
According to another embodiment, the aqueous composition comprises, a pH under 5.0 and,
(a) a carboxylic acid polymer comprising polymerized unsaturated carboxylic acid monomers having a number average molecular weight of about 20,000 to 1,500,000 or blends of high and low number average molecular weight polymers of polymerized unsaturated carboxylic acid monomers,
(b) 1 to 15% by weight of an oxidizing agent,
(c) up to 3.0% by weight of abrasive particles,
(d) 50-5,000 ppm (parts per million) of a corrosion inhibitor,
(e) up to 3.0% by weight of a complexing agent, such as, malic acid, and
(f) 0.1 to 5.0% by weight of a surfactant.
A polishing composition according to the invention can be used with conventional polishing equipment, known polishing pads and techniques to polish semiconductor wafers having copper circuits that result in clearing of a layer of excess copper from the surface of the wafer with a substantial reduction in dishing of the copper circuits of the wafer. The polishing composition provides a substantially planar surface that is free from scratches and other defects that commonly result from polishing.
The polishing composition is an aqueous composition that has a pH under 5.0 and preferably has a pH of 2.8 to 4.2 and more preferably, a pH of 2.8 to 3.8.
The polishing composition contains 1-15% by weight of an oxidizing agent that serves as an oxidizer of the metal at a pH lower than 5.0. Appropriate oxidizing agents are hydrogen peroxide, iodates, such as, potassium iodate, nitrates, such as, cesium nitrate, barium nitrate, ammonium nitrate, mixtures of ammonium nitrate and cesium nitrate, carbonates, such as, ammonium carbonate, persulfates, such as, ammonium and sodium persulfate, and perchlorates. For example, the polishing composition contains about 5-10% by weight of an oxidizing agent. Preferably, the polishing composition contains about 9% by weight of hydrogen peroxide as the oxidizing agent.
The composition contains up to 3.0% by weight and preferably, 0.1-1.0% by weight of a complexing agent, such as, a dissolved carboxylic acid having two or more carboxyl groups and having a hydroxyl group as disclosed in U.S. Pat. No. 5,391,258. An appropriate complexing agent includes straight chain mono- and dicarboxylic acids and their salts, such as, malic acid and malates, tartaric acid and tartarates, gluconic acid and gluconates, citric acid and citrates, malonic acid and malonates, formic acid and formates, lactic acid and lactates. Polyhydroxybenzoic acid, phthalic acid and salts thereof also can be used. During CMP, the oxidizing agent serves as an oxidizer of the metal at said pH under 5.0 to provide ions of the metal. The complexing agent dissolves the ions, while the polishing pad applies downforce and abrasion to the metal being polished. As a result, the metal layer is removed from the underlying barrier film.
The polishing composition contains 50 to 5,000 ppm (parts per million) of an inhibitor preferably BTA (benzotriazole), or TTA (tolyltriazole) or mixtures thereof. Other inhibitors that can be used are 1-hydroxybenzotriazole, N-(1H-benzotriazole-1-ylmethyl) formamide, 3,5-dimethylpyrazole, indazole, 4-bromopyrazole, 3-amino-5-phenylpyrazole, 3-amino-4-pyrazolecarbonitrile, 1-methylimidazole, Indolin QTS and the like. It is known that the inhibitor, for example, benzotriazole (BTA), adsorbs on the surface of a metal, for example, copper, to inhibit corrosion of the metal, for example, by exposure of the metal to the atmosphere. The inhibitor tends to lower a tendency for the oxidizer of the metal to provide ions of the metal.
The aqueous composition comprises, a carboxylic acid polymer, which maximizes the removal rate of the metal during CMP. It is believed that the carboxylic acid polymer is reactive on the metal similarly as particle abrasives are reactive on the metal, in transferring energy from a polishing pad to the copper metal, which removes the copper metal at an increased removal rate during CMP.
Advantageously, the aqueous composition provided with the carboxylic acid polymer removes or minimizes copper metal residuals on an underlying barrier film. Residuals refers to spots of the metal remaining on the underlying barrier film after completion of a CMP cycle.
A further embodiment of the polishing composition is provided with, up to 3% by weight of abrasive particles. According to a further embodiment, from 0.01% up to 3% by weight of abrasive particles are present. Appropriate abrasive particles are those that are appropriately used in CMP polishing of semiconductors, such as, alumina, silica, ceria, germania, diamond, silicon carbide, titania, zirconia, boron nitride, boron carbide and various mixtures of any of the above. The aqueous composition comprises, a carboxylic acid polymer, which increases the removal rate of the metal during CMP, to a maximum beyond the removal rate provided by the abrasive particles in the absence of the carboxylic acid polymer.
One of the disadvantages of an aqueous composition provided with the carboxylic acid polymer, is that the carboxylic acid polymer is reactive with the metal in trenches, which tends to provide a relatively high removal rate of the metal in trenches, despite the polishing pad applying a relatively lower downforce on the metal in trenches. The high removal rate of the metal in trenches would cause unwanted dishing.
An embodiment of the aqueous composition comprises, a combination of a metal corrosion inhibitor and a surfactant, which adsorbs on the metal in trenches on which the relatively lower downforce is applied, to minimize the removal rate of the metal in trenches, as would tend to be provided by the carboxylic acid polymer in the absence of the combination of the metal corrosion inhibitor and the surfactant.
The terminology, surfactant, is interpreted to mean, a surface active agent that adsorbs to a surface and lowers a surface tension of a liquid on the surface. According to an embodiment, a surfactant comprises, an anionic surfactant as distinguished from a cationic surfactant, and as distinguished from a neutral charge surfactant.
According to another embodiment, a surfactant comprises, a sulfonate surfactant comprised of molecules having at least six carbon atoms, as distinguished from a sulfonate comprising molecules having an insufficient number of carbon atoms to exist as a polymer in the polishing composition.
According to another embodiment, a surfactant comprises, an alkali metal organic sulfonate. An embodiment of the polishing composition contains 0.1-5% by weight of an alkali metal organic sulfonate surfactant. Preferably, the alkali metal of the alkali metal organic sulfonate surfactant is selected from sodium, potassium and lithium and the organic group is an aliphatic group having 2-16 carbon atoms. One preferred surfactant is sodium octane sulfonate. Other useful surfactants are potassium octane sulfonate, lithium octane sulfonate and sodium dodecyl sulfonate.
Appropriate other anionic surfactants include, sulfates, phosphates and carboxylates in place of or in combination with the aforementioned sulfonate surfactants.
It is theorized that a combination of the corrosion inhibitor and the surfactant provides a relatively large reduction in metal removal rate with relatively small reductions in downforce applied by the polishing pad on the metal being polished. Where the metal layer is relatively higher in elevation than the metal in trenches, the downforce is relatively higher, and the metal removal rate is maximized by the polishing composition having the combination of the corrosion inhibitor and the surfactant. Where the metal layer is relatively low in elevation, including the metal in trenches being relatively low in elevation, the downforce is relatively lower, and the combination of a metal corrosion inhibitor and a surfactant, adsorbs on the metal in trenches on which the relatively lower downforce is applied, to minimize the removal rate of the metal in trenches, as would tend to be provided by the carboxylic acid polymer and the applied downforce without the combination of the metal corrosion inhibitor and the surfactant. Thus, dishing is minimized due to the minimized removal rate of the metal in trenches. Further, the higher elevations are removed at a higher removal rate than that of the lower elevations, which means that planarization is attained quickly during a CMP operation. Planarization refers to a smooth, planar polished surface with minimized elevation differences on the polished semiconductor substrate, as provided by CMP.
For example, BTA as the corrosion inhibitor would cover the metal layer with a monomolecular layer or multimolecular layer film of BTA, in the absence of the surfactant. The combination of the corrosion inhibitor with the surfactant adsorbs to provide a disturbed film of BTA, due to competing adsorption of both the corrosion inhibitor and the surfactant. The relatively higher downforce removes the disturbed film of BTA, while a relatively lower downforce slowly removes the disturbed film of BTA.
The polishing composition may further contain pH buffers, such as, amines, and may contain surfactants, deflocculants, viscosity modifiers, wetting agents, cleaning agents and the like.
The following description refers to sources of the carboxylic acid polymer. The polishing composition contains about 0.05-2.0% by weight, based on the weight of the composition, of a carboxylic acid polymer comprising, polymerized unsaturated carboxylic acid monomers having a number average molecular weight of about 20,000 to 1,500,000. The number average molecular weight is determined by GPC (gel permeation chromatography). Appropriate embodiments comprise, blends of high and low number average molecular weight carboxylic acid polymers. These carboxylic acid polymers are either, in solution, or in the form of an aqueous dispersion. Appropriate unsaturated carboxylic acid monomers include, unsaturated monocarboxylic acids and unsaturated dicarboxylic acids and water soluble acid salts as the source of such acids. Appropriate unsaturated monocarboxylic acid monomers contain 3-6 carbon atoms, and comprise, acrylic acid, oligomeric acrylic acid, methacrylic acid, crotonic acid and vinyl acetic acid. Appropriate unsaturated dicarboxylic acids include the anhydrides thereof, which contain 4-8 carbon atoms, and comprise, for example, maleic acid, maleic anhydride, fumaric acid, glutaric acid, itaconic acid, itaconic anhydride, and cyclohexene dicarboxylic acid.
Further embodiments comprise, poly(meth)acrylic acids having a number average molecular weight of about 20,000 to 150,000, preferably 25,000 to 75,000 and more preferably, 25,000 to 40,000. Blends of high and low number average molecular weight poly(meth)acrylic acids comprise further embodiments. In such blends or mixtures of poly(meth)acrylic acids, a low number average molecular weight poly(meth)acrylic acid of 20,000 to 100,000 and preferably, 20,000 to 40,000 is in a combination with a high average poly(meth)acrylic acid having a number average molecular weight of 200,000 to 150,000, preferably 150,000 to 300,000. Appropriately, the weight ratio of the low number average molecular weight poly(meth)acrylic acid to the high number average molecular weight poly(meth)acrylic acid is 10:1 to 1:10, preferably 4:1 to 1:4, and more preferably 2:1 to 1:2.
An embodiment comprises, a polyacrylic acid having a number average molecular weight of about 30,000 and a polyacrylic acid having a number average molecular weight of about 250,000 in a 1:1 weight ratio.
The term xe2x80x9cpoly(meth)acrylic acidxe2x80x99, as used herein, means, polymers of acrylic acid or polymers of methacrylic acid. According to an embodiment, very low number average molecular weight poly(meth)acrylic acid polymers are present in the aforementioned blend. Examples of such polymers are poly(meth)acrylic acid polymers having a number average molecular weight of 1,000 to 5,000.
According to an embodiment, the aqueous composition is provided with high carboxylic acid containing copolymers and terpolymers, in which the carboxylic acid component comprises 5-75% by weight of the polymer. An appropriate polymer comprises one of, polymers of (meth)acrylic acid and acrylamide or methacrylamide; polymers of (meth)acrylic acid and styrene and other vinyl aromatic monomers; polymers of alkyl (meth)acrylates (esters of acrylic or methacrylic acid) and a mono or dicarboxylic acid, such as, acrylic or methacrylic acid or itaconic acid; polymers of substituted vinyl aromatic monomers having substituents, such as, halogen, i.e., chlorine, fluorine, bromine, nitro, cyano, alkoxy, haloalkyl, carboxy, amino, amino alkyl and a unsaturated mono or dicarboxylic acid and an alkyl (meth)acrylate; polymers of monethylenically unsaturated monomers containing a nitrogen ring, such as, vinyl pyridine, alkyl vinyl pyridine, vinyl butyrolactam, vinyl caprolactam, and an unsaturated mono or dicarboxylic acid; polymers of olefins, such as, propylene, isobutylene, or long chain alkyl olefins having 10 to 20 carbon atoms and an unsaturated mono or dicarboxylic acid; polymers of vinyl alcohol esters, such as, vinyl acetate and vinyl stearate or vinyl halides, such as, vinyl fluoride, vinyl chloride, vinylidene fluoride or vinyl nitriles, such as, acrylonitrile and methacrylonitrile and an unsaturated mono or dicarboxylic acid; polymers of alkyl (meth) acrylates having 1-24 carbon atoms in the alkyl group and an unsaturated monocarboxylic acid, such as, acrylic acid or methacrylic acid.
A further embodiment comprises an aqueous composition provided with polymers that are degradable, for example, biodegradable or photodegradable. An example of such a composition that is biodegradable is a polyacrylic acid polymer containing segments of poly(acrylate co methyl 2-cyanoacrylate).
The following are appropriate polishing pads that can be used with the polishing composition of this invention to polish copper containing semiconductors: a metals pad described in Roberts et al. U.S. Pat. No. 6,022,268, issued Feb. 8, 2000, a polishing pad containing particles for polishing described in Cook et al. U.S. Pat. No. 5,489,233, issued Feb. 6, 1996, a polishing pad of polymer impregnated fiber matrices sold by Rodel Inc. under the trade name xe2x80x9cSUBAxe2x80x9d, a pad of a polymer sheet containing void spaces formed by in situ production or incorporation of hollow fill materials (appropriate of such a pad are those sold by Rodel Inc. under the trade names xe2x80x9cPOLITEXxe2x80x9d and xe2x80x9cIC 1010xe2x80x9d), a pad of polymer sheets containing solid particles that are added as fillers that may optionally contain void spaces, effected either by in situ production or by incorporation of hollow filler materials (appropriate of such pads are those sold by Rodel Inc. under the trade name xe2x80x9cMHxe2x80x9d), and a composite pad of multiple layers of materials whose outer substrate that contacts the surface of the semiconductor being polished is one of the pads selected from the above.
The following examples illustrate the invention. All parts and percentages are on a weight basis and unless otherwise indicated and molecular weights are determined by gel permeation chromatography unless otherwise indicated.